Begin by having a MakerBot extrude plastic coins, then compact the plastic coin in sand to produce a mold. Heat up your bronze in a trashcan furnace and pour it into the mold. The plastic melts away and you’re left with a bronze coin.

There are probably some safety measures and precautions that should be followed as well…

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16 thoughts on “Bronze casting with MakerBot”

medallion would be better than coin and to complete the cycle infill part of the medallion using the makerbot. dont forget to embed a rfid chip in the infill plastic for key-less access to the new hackerspace!!!

that’s great! having done a lot of lost-wax and lost-styrofoam casting, i’m a big fan! if you could get the makerbot to extrude in styrofoam, you might end up with a casting with sharper edges and more detail due to the more rapid vaporization.

Only partially related, but I got an e-mail from a rapid proto company that does 17-4PH stainless steel at basically full strength. I had them ship me some samples… and man, this is the future. The parts looked pretty good, and the surface finish after polishing was great. As additive manufacturing machines become more common and cheaper, they’re going to take the world by storm. This stuff really will change the world.

Seems like laser sintering is the way to go. I wish we could get a makerbot that could do that!

High powered lasers are still pricey… but they’re going down! They’re working on 100KW (yes… 100KW) solid state lasers for weapons, and were up to like 60KW two years ago. As we advance this technology and simplify solid state lasers… we’ll be able to make SLS machines on a budget just like MakerBots now.

They actually didn’t use a lost-pattern process at all. The article mentions wooden frames (plural) and parting dust, which means they used a standard two-part, green sand mold. Lost-wax is mentioned, though, so I can understand the confusion.

@David: It wouldn’t “go boom” without the oxidizing power of rust (cf. thermite) but it would still oxidize into uselessness, unless you did it in an inert atmosphere, like nitrogen, or no atmosphere i.e. a vacuum.

I read in PopSci or somewhere a few years back about a selective sintering unit that used a focused halogen lamp instead of a laser. I can’t find the mag or info online… Anyone know more about this? It sounds doable in a makerbot-style hobbyist machine (maybe not fusing metal, but some kind of plastic powder, at least).

This write-up is a little misleading. I work with Dave at QC Co-Lab, and he’s doing green sand casting, in a similar process to the foundry 101 link. We reuse the plastic piece, impressing a new sand form for each bronze piece. Lost wax casting is capable of much more accurate reproduction, but the mold is destroyed with each piece.

We do all the hot work outdoors in a shaded area to avoid fumes. Being out of direct sunlight makes it easier to gauge the temperature of the metal. Models with a draft or taper will part from the mold easily, giving a better cast – we had to tweak draft angles and feature sizes to get good detail, one reason the coins turned into medallions:) Some light sanding on the plastic helped, too.

@Drake All (or at least most) solid metals are crystalline, it’s just that most of the time, the metal is made up of many small grains with their crystal lattices oriented in different directions. Certain applications can’t tolerate this, so they employ heat treatment methods to cause all the grains to either grow or shrink, until there is only one grain. Sometimes in steel you can see what appears to be a camouflage pattern of different colors and reflectances. This occurs because large grains of the steel are oriented along different axes with respect to each other and the light, so they interact with the light differently.